1. Field of the Invention
The present invention relates to a raw material for a complex perovskite ceramic composition for use in electronic materials and a process for preparing the ceramic composition.
2. Description of the Prior Art
Complex perovskite compounds containing lead (Pb) have been widely used in dielectric materials and piezo-electric materials. The dielectric materials have been mainly used in multilayer ceramic capacitors. For example, in Japanese Patent Application Laid-Open No. 42167/1982, a ceramic composition comprising Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 --PbTiO.sub.3 --Pb(Ni.sub.1/3 Nb.sub.2/3)O.sub.3 has been disclosed, and in Japanese Patent Application Laid-Open No. 74569/1983, a ceramic composition comprising Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 --PbTiO.sub.3 has been disclosed.
As the composite perovskite compounds for use in the piezo-electric materials, Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 --PbTiO.sub.3, Pb(Zn.sub.1/3 Nb.sub.2/3)O.sub.3 --PbTiO.sub.3 and the like are known. To the complex perovskite compounds containing lead, manganese has often been added.
For example, the dielectric materials have been used for the prevention of the deterioration of insulation resistance or for the improvement of temperature characteristics of dielectric constant On the other hand, as the piezo-electric materials, there have been reported characteristic compositions of composite perovskite compounds containing Mn. For example, in Japanese Patent Application Laid-Open No. 103486/1981, (Pb, Sr)TiO.sub.3 --(Mn1/3Sb.sub.2/3)O.sub.3 and the like have been disclosed.
In the case that a trace amount of Mn is added to the ceramic composition, manganese carbonate (MnCO.sub.3) or MnO.sub.2 has often been used as a raw material which is insoluble in water and which has a small particle diameter, if water is used as a dispersant.
On the other hand, there has been reported an example where a composite oxide as a raw material is used as one means for increasing a ratio of a product phase of a perovskite phase and for improving dielectric properties. For example, in Mat. Res. Bull., No. 17, p. 1245 (1982), Swartz et al. have reported that the employment of MgNb.sub.2 O.sub.6 in a Pb(Mg.sub.1/3 Nb.sub.2/3)O.sub.3 system is effective to improve the dielectric properties, and on the other hand, Japanese Patent Application Laid-Open No. 94649/1989 has disclosed that it is effective for the improvement of the dielectric properties to use MgWO.sub.4 in a Pb(Mg.sub.1/2 W.sub.1/2)O.sub.3 system.
Since the amount of Mn to be added or to be replaced is usually several mol % or less in terms of MnO, it is difficult to uniformly mix the same. As a means for uniformly mixing the trace amount of the component in the complex perovskite compound containing Mn, for example, Japanese Patent Application Laid-Open No. 54122/1991 has disclosed a technique for improving the characteristics by doing, in a solution, a synthesis with an organic metal compound such as a metal alkoxide as a raw material.
However, when the synthesis is done by this technique, it is required to use a more expensive organic metal oxide as the raw material than a usual oxide, which is industrially disadvantageous.